Method and Apparatus for Decoding an Audio Signal

ABSTRACT

An apparatus for decoding an audio signal and method thereof are disclosed. The present invention includes receiving the audio signal and spatial information, identifying a type of modified spatial information, generating the modified spatial information using the spatial information, and decoding the audio signal using the modified spatial information, wherein the type of the modified spatial information includes at least one of partial spatial information, combined spatial information and expanded spatial information. Accordingly, an audio signal can be decoded into a configuration different from a configuration decided by an encoding apparatus. Even if the number of speakers is smaller or greater than that of multi-channels before execution of downmixing, it is able to generate output channels having the number equal to that of the speakers from a downmix audio signal.

TECHNICAL FIELD

The present invention relates to audio signal processing, and moreparticularly, to an apparatus for decoding an audio signal and methodthereof. Although the present invention is suitable for a wide scope ofapplications, it is particularly suitable for decoding audio signals.

BACKGROUND ART

Generally, when an encoder encodes an audio signal, in case that theaudio signal to be encoded is a multi-channel audio signal, themulti-channel audio signal is downmixed into two channels or one channelto generate a downmix audio signal and spatial information is extractedfrom the multi-channel audio signal. The spatial information is theinformation usable in upmixing the multi-channel audio signal from thedownmix audio signal. Meanwhile, the encoder downmixes a multi-channelaudio signal according to a predetermined tree configuration. In thiscase, the predetermined tree configuration can be the structure(s)agreed between an audio signal decoder and an audio signal encoder. Inparticular, if identification information indicating a type of one ofthe predetermined tree configurations is present, the decoder is able toknow a structure of the audio signal having been upmixed, e.g., a numberof channels, a position of each of the channels, etc.

Thus, if an encoder downmixes a multi-channel audio signal according toa predetermined tree configuration, spatial information extracted inthis process is dependent on the structure as well. So, in case that adecoder upmixes the downmix audio signal using the spatial informationdependent on the structure, a multi-channel audio signal according tothe structure is generated. Namely, in case that the decoder uses thespatial information generated by the encoder as it is, upmixing isperformed according to the structure agreed between the encoder and thedecoder only. So, it is unable to generate an output-channel audiosignal failing to follow the agreed structure. For instance, it isunable to upmix a signal into an audio signal having a channel numberdifferent (smaller or greater) from a number of channels decidedaccording to the agreed structure.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention is directed to an apparatus fordecoding an audio signal and method thereof that substantially obviateone or more of the problems due to limitations and disadvantages of therelated art.

An object of the present invention is to provide an apparatus fordecoding an audio signal and method thereof, by which the audio signalcan be decoded to have a structure different from that decided by anencoder.

Another object of the present invention is to provide an apparatus fordecoding an audio signal and method thereof, by which the audio signalcan be decoded using spatial information generated from modifying formerspatial information generated from encoding.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method ofdecoding an audio signal according to the present invention includesreceiving the audio signal and spatial information, identifying a typeof modified spatial information, generating the modified spatialinformation using the spatial information, and decoding the audio signalusing the modified spatial information, wherein the type of the modifiedspatial information includes at least one of partial spatialinformation, combined spatial information and expanded spatialinformation.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of decoding an audio signalincludes receiving spatial information, generating combined spatialinformation using the spatial information, and decoding the audio signalusing the combined spatial information, wherein the combined spatialinformation is generated by combining spatial parameters included in thespatial information.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of decoding an audio signalincludes receiving spatial information including at least one spatialinformation and spatial filter information including at least one filterparameter, generating combined spatial information having a surroundeffect by combining the spatial parameter and the filter parameter, andconverting the audio signal to a virtual surround signal using thecombined spatial information.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, a method of decoding an audio signalincludes receiving the audio signal, receiving spatial informationincluding tree configuration information and spatial parameters,generating modified spatial information by adding extended spatialinformation to the spatial information, and upmixing the audio signalusing the modified spatial information, which comprises includingconverting the audio signal to a primary upmixed audio signal based onthe spatial information and converting the primary upmixed audio signalto a secondary upmixed audio signal based on the extended spatialinformation.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a block diagram of an audio signal encoding apparatus and anaudio signal decoding apparatus according to the present invention;

FIG. 2 is a schematic diagram of an example of applying partial spatialinformation;

FIG. 3 is a schematic diagram of another example of applying partialspatial information;

FIG. 4 is a schematic diagram of a further example of applying partialspatial information;

FIG. 5 is a schematic diagram of an example of applying combined spatialinformation;

FIG. 6 is a schematic diagram of another example of applying combinedspatial information;

FIG. 7 is a diagram of sound paths from speakers to a listener, in whichpositions of the speakers are shown;

FIG. 8 is a diagram to explain a signal outputted from each speakerposition for a surround effect;

FIG. 9 is a conceptional diagram to explain a method of generating a3-channel signal using a 5-channel signal;

FIG. 10 is a diagram of an example of configuring extended channelsbased on extended channel configuration information;

FIG. 11 is a diagram to explain a configuration of the extended channelsshown in FIG. 10 and the relation with extended spatial parameter;

FIG. 12 is a diagram of positions of a multi-channel audio signal of5.1-channels and an output channel audio signal of 6.1-channels;

FIG. 13 is a diagram to explain the relation between a virtual soundsource position and a level difference between two channels;

FIG. 14 is a diagram to explain levels of two rear channels and a levelof a rear center channel;

FIG. 15 is a diagram to explain a position of a multi-channel audiosignal of 5.1-channels and a position of an output channel audio signalof 7.1-channels;

FIG. 16 is a diagram to explain levels of two left channels and a levelof a left front side channel (Lfs); and

FIG. 17 is a diagram to explain levels of three front channels and alevel of a left front side channel (Lfs).

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

General terminologies used currently and globally are selected asterminologies used in the present invention. And, there areterminologies arbitrarily selected by the applicant for special cases,for which detailed meanings are explained in detail in the descriptionof the preferred embodiments of the present invention. Hence, thepresent invention should be understood not with the names of theterminologies but with the meanings of the terminologies.

First of all, the present invention generates modified spatialinformation using spatial information and then decodes an audio signalusing the generated modified spatial information. In this case, thespatial information is spatial information extracted in the course ofdownmixing according to a predetermined tree configuration and themodified spatial information is spatial information newly generatedusing spatial information.

The present invention will be explained in detail with reference to FIG.1 as follows.

FIG. 1 is a block diagram of an audio signal encoding apparatus and anaudio signal decoding apparatus according to an embodiment of thepresent invention.

Referring to FIG. 1, an apparatus for encoding an audio signal(hereinafter abbreviated an encoding apparatus) 100 includes adownmixing unit 110 and a spatial information extracting unit 120. And,an apparatus for decoding an audio signal (hereinafter abbreviated adecoding apparatus) 200 includes an output channel generating unit 210and a modified spatial information generating unit 220.

The downmixing unit 110 of the encoding apparatus 100 generates adownmix audio signal d by downmixing a multi-channel audio signal IN_M.The downmix audio signal d can be a signal generated from downmixing themulti-channel audio signal IN_M by the downmixing unit 110 or anarbitrary downmix audio signal generated from downmixing themulti-channel audio signal IN_M arbitrarily by a user.

The spatial information extracting unit 120 of the encoding apparatus100 extracts spatial information s from the multi-channel audio signalIN_M. In this case, the spatial information is the information needed toupmix the downmix audio signal d into the multi-channel audio signalIN_M.

Meanwhile, the spatial information can be the information extracted inthe course of downmixing the multi-channel audio signal IN_M accordingto a predetermined tree configuration. In this case, the treeconfiguration may correspond to tree configuration(s) agreed between theaudio signal decoding and encoding apparatuses, which is not limited bythe present invention.

And, the spatial information is able to include tree configurationinformation, an indicator, spatial parameters and the like. The treeconfiguration information is the information for a tree configurationtype. So, a number of multi-channels, a per-channel downmixing sequenceand the like vary according to the tree configuration type. Theindicator is the information indicating whether extended spatialinformation is present or not, etc. And, the spatial parameters caninclude channel level difference (hereinafter abbreviated CLD) in thecourse of downmixing at least two channels into at most two channels,inter-channel correlation or coherence (hereinafter abbreviated ICC),channel prediction coefficients (hereinafter abbreviated CPC) and thelike.

Meanwhile, the spatial information extracting unit 120 is able tofurther extract extended spatial information as well as the spatialinformation. In this case, the extended spatial information is theinformation needed to additionally extend the downmix audio signal dhaving been upmixed with the spatial parameter. And, the extendedspatial information can include extended channel configurationinformation and extended spatial parameters. The extended spatialinformation, which shall be explained later, is not limited to the oneextracted by the spatial information extracting unit 120.

Besides, the encoding apparatus 100 is able to further include a corecodec encoding unit (not shown in the drawing) generating a downmixedaudio bitstream by decoding the downmix audio signal d, a spatialinformation encoding unit (not shown in the drawing) generating aspatial information bitstream by encoding the spatial information s, anda multiplexing unit (not shown in the drawing) generating a bitstream ofan audio signal by multiplexing the downmixed audio bitstream and thespatial information bitstream, on which the present invention does notput limitation.

And, the decoding apparatus 200 is able to further include ademultiplexing unit (not shown in the drawing) separating the bitstreamof the audio signal into a downmixed audio bitstream and a spatialinformation bitstream, a core codec decoding unit (not shown in thedrawing) decoding the downmixed audio bitstream, and a spatialinformation decoding unit (not shown in the drawing) decoding thespatial information bitstream, on which the present invention does notput limitation.

The modified spatial information generating unit 220 of the decodingapparatus 200 identifies a type of the modified spatial informationusing the spatial information and then generates modified spatialinformation s′ of a type that is identified based on the spatialinformation. In this case, the spatial information can be the spatialinformation s conveyed from the encoding apparatus 100. And, themodified spatial information is the information that is newly generatedusing the spatial information.

Meanwhile, there can exist various types of the modified spatialinformation. And, the various types of the modified spatial informationcan include at least one of a) partial spatial information, b) combinedspatial information, and c) extended spatial information, on which nolimitation is put by the present invention.

The partial spatial information includes spatial parameters in part, thecombined spatial information is generated from combining spatialparameters, and the extended spatial information is generated using thespatial information and the extended spatial information.

The modified spatial information generating unit 220 generates themodified spatial information in a manner that can be varied according tothe type of the modified spatial information. And, a method ofgenerating modified spatial information per a type of the modifiedspatial information will be explained in detail later.

Meanwhile, a reference for deciding the type of the modified spatialinformation may correspond to tree configuration information in spatialinformation, indicator in spatial information, output channelinformation or the like. The tree configuration information and theindicator can be included in the spatial information s from the encodingapparatus. The output channel information is the information forspeakers interconnecting to the decoding apparatus 200 and can include anumber of output channels, position information for each output channeland the like. The output channel information can be inputted in advanceby a manufacturer or inputted by a user.

A method of deciding a type of modified spatial information using thesesinformations will be explained in detail later.

The output channel generating unit 210 of the decoding apparatus 200generates an output channel audio signal OUT_N from the downmix audiosignal d using the modified spatial information s′.

The spatial filter information 230 is the information for sound pathsand is provided to the modified spatial information generating unit 220.In case that the modified spatial information generating unit 220generates combined spatial information having a surround effect, thespatial filter information can be used.

Hereinafter, a method of decoding an audio signal by generating modifiedspatial information per a type of the modified spatial information isexplained in order of (1) Partial spatial information, (2) Combinedspatial information, and (3) Expanded spatial information as follows.

(1) Partial Spatial Information

Since spatial parameters are calculated in the course of downmixing amulti-channel audio signal according to a predetermined treeconfiguration, an original multi-channel audio signal before downmixingcan be reconstructed if a downmix audio signal is decoded using thespatial parameters intact. In case of attempting to make a channelnumber N of an output channel audio signal be smaller than a channelnumber M of a multi-channel audio signal, it is able to decode a downmixaudio signal by applying the spatial parameters in part.

This method can be varied according to a sequence and method ofdownmixing a multi-channel audio signal in an encoding apparatus, i.e.,a type of a tree configuration. And, the tree configuration type can beinquired using tree configuration information of spatial information.And, this method can be varied according to a number of output channels.Moreover, it is able to inquire the number of output channels usingoutput channel information.

Hereinafter, in case that a channel number of an output channel audiosignal is smaller than a channel number of a multi-channel audio signal,a method of decoding an audio signal by applying partial spatialinformation including spatial parameters in part is explained by takingvarious tree configurations as examples in the following description.

(1)-1. First Example of Tree configuration (5-2-5 Tree Configuration)

FIG. 2 is a schematic diagram of an example of applying partial spatialinformation.

Referring to a left part of FIG. 2, a sequence of downmixing amulti-channel audio signal having a channel number 6 (left front channelL, left surround channel L_(s), center channel C, low frequency channelLFE, right front channel R, right surround channel R_(s)) into stereodownmixed channels L_(o) and R_(o) and the relation between themulti-channel audio signal and spatial parameters are shown.

First of all, downmixing between the left channel L and the leftsurround channel L_(s), downmixing between the center channel C and thelow frequency channel LFE and downmixing between the right channel R andthe right surround channel R_(s) are carried out. In this primarydownmixing process, a left total channel L_(t), a center total channelC_(t) and a right total channel R_(t) are generated. And, spatialparameters calculated in this primary downmixing process include CLD₂(ICC₂ inclusive), CLD₁ (ICC₁ inclusive), CLD₀ (ICC₀ inclusive), etc.

In a secondary process following the primary downmixing process, theleft total channel L_(t), the center total channel C_(t) and the righttotal channel R_(t) are downmixed together to generate a left channelL_(o) and a right channel R_(o). And, spatial parameters calculated inthis secondary downmixing process are able to include CLD_(TTT),CPC_(TTT), ICC_(TTT), etc.

In other words, a multi-channel audio signal of total six channels isdownmixed in the above sequential manner to generate the stereodownmixed channels L_(o) and R_(o).

If the spatial parameters (CLD₂, CLD₁, CLD₀, CLD_(TTT), etc.) calculatedin the above sequential manner are used as they are, they are upmixed insequence reverse to the order for the downmixing to generate themulti-channel audio signal having the channel number of 6 (left frontchannel L, left surround channel L_(s), center channel C, low frequencychannel LFE, right front channel R, right surround channel R_(s)).

Referring to a right part of FIG. 2, in case that partial spatialinformation corresponds to CLD_(TTT) among spatial parameters (CLD₂,CLD₁, CLD₀, CLD_(TTT), etc.), it is upmixed into the left total channelL_(t), the center total channel C_(t) and the right total channel R_(t).If the left total channel L_(t) and the right total channel R_(t) areselected as an output channel audio signal, it is able to generate anoutput channel audio signal of two channels L_(t) and R_(t). If the lefttotal channel L_(t), the center total channel C_(t) and the right totalchannel R_(t) are selected as an output channel audio signal, it is ableto generate an output channel audio signal of three channels L_(t),C_(t) and R_(t). After upmixing has been performed using CLD₁ inaddition, if the left total channel L_(t), the right total channelR_(t), the center channel C and the low frequency channel LFE areselected, it is able to generate an output channel audio signal of fourchannels (L_(t), R_(t), C and LFE).

(1)-2. Second Example of Tree Configuration (5-1-5 Tree Configuration)

FIG. 3 is a schematic diagram of another example of applying partialspatial information.

Referring to a left part of FIG. 3, a sequence of downmixing amulti-channel audio signal having a channel number 6 (left front channelL, left surround channel L_(s), center channel C, low frequency channelLFE, right front channel R, right surround channel R_(s)) into a monodownmix audio signal M and the relation between the multi-channel audiosignal and spatial parameters are shown.

First of all, like the first example, downmixing between the leftchannel L and the left surround channel L_(s), downmixing between thecenter channel C and the low frequency channel LFE and downmixingbetween the right channel R and the right surround channel R_(s) arecarried out. In this primary downmixing process, a left total channelL_(t), a center total channel C_(t) and a right total channel R_(t) aregenerated. And, spatial parameters calculated in this primary downmixingprocess include CLD₃ (ICC₃ inclusive), CLD₄ (ICC₄ inclusive), CLD₅ (ICC₅inclusive), etc. (in this case, CLD_(x) and ICC_(x) are discriminatedfrom the former CLD_(x) in the first example).

In a secondary process following the primary downmixing process, theleft total channel L_(t) and the right total channel R_(t) are downmixedtogether to generate a left center channel LC, and the center totalchannel C_(t) and the right total channel R_(t) are downmixed togetherto generate a right center channel RC. And, spatial parameterscalculated in this secondary downmixing process are able to include CLD₂(ICC₂ inclusive), CLD₁ (ICC₁ inclusive), etc.

Subsequently, in a tertiary downmixing process, the left center channelLC and the right center channel R_(t) are downmixed to generate a monodownmixed signal M. And, spatial parameters calculated in the tertiarydownmixing process include CLD₀ (ICC₀ inclusive), etc.

Referring to a right part of FIG. 3, in case that partial spatialinformation corresponds to CLD₀ among spatial parameters (CLD₃, CLD₄,CLD₅, CLD₁, CLD₂, CLD₀, etc.), a left center channel LC and a rightcenter channel RC are generated. If the left center channel LC and theright center channel RC are selected as an output channel audio signal,it is able to generate an output channel audio signal of two channels LCand RC.

Meanwhile, if partial spatial information corresponds to CLD₀, CLD₁ andCLD₂, among spatial parameters (CLD₃, CLD₄, CLD₅, CLD₁, CLD₂, CLD₀,etc.), a left total channel L_(t), a center total channel C_(t) and aright total channel R_(t) are generated.

If the left total channel L_(t) and the right total channel R_(t) areselected as an output channel audio signal, it is able to generate anoutput channel audio signal of two channels L_(t) and R_(t). If the lefttotal channel L_(t), the center total channel C_(t) and the right totalchannel R_(t) are selected as an output channel audio signal, it is ableto generate an output channel audio signal of three channels L_(t),C_(t) and R_(t).

In case that partial spatial information includes CLD₄ in addition,after upmixing has been performed up to a center channel and a lowfrequency channel LFE, if the left total channel L_(t), the right totalchannel R_(t), the center channel C and the low frequency channel LFEare selected as an output channel audio signal, it is able to generatean output channel audio signal of four channels (L_(t), R_(t), C andLFE).

(1)-3. Third Example of Tree Configuration (5-1-5 Tree Configuration)

FIG. 4 is a schematic diagram of a further example of applying partialspatial information.

Referring to a left part of FIG. 4, a sequence of downmixing amulti-channel audio signal having a channel number 6 (left front channelL, left surround channel L_(s), center channel C, low frequency channelLFE, right front channel R, right surround channel R_(s)) into a monodownmix audio signal M and the relation between the multi-channel audiosignal and spatial parameters are shown.

First of all, like the first or second example, downmixing between theleft channel L and the left surround channel L_(s), downmixing betweenthe center channel C and the low frequency channel LFE and downmixingbetween the right channel R and the right surround channel R_(s) arecarried out. In this primary downmixing process, a left total channelL_(t), a center total channel C_(t) and a right total channel R_(t) aregenerated. And, spatial parameters calculated in this primary downmixingprocess include CLD₁ (ICC₁ inclusive), CLD₂ (ICC₂ inclusive), CLD₃ (ICC₃inclusive), etc. (in this case, CLD_(x) and ICC_(x) are discriminatedfrom the former CLD_(x) and ICC_(x) in the first or second example).

In a secondary process following the primary downmixing process, theleft total channel L_(t), the center total channel C_(t) and the righttotal channel R_(t) are downmixed together to generate a left centerchannel LC and a right channel R. And, a spatial parameter CLD_(TTT)(ICC_(TTT) inclusive) is calculated.

Subsequently, in a tertiary downmixing process, the left center channelLC and the right channel R are downmixed to generate a mono downmixedsignal M. And, a spatial parameter CLD₀ (ICCo inclusive) is calculated.

Referring to a right part of FIG. 4, in case that partial spatialinformation corresponds to CLD₀ and CLD_(TTT) among spatial parameters(CLD₁, CLD₂, CLD₃, CLD_(TTT), CLD₀, etc.), a left total channel L_(t), acenter total channel C_(t) and a right total channel R_(t) aregenerated.

If the left total channel L_(t) and the right total channel R_(t) areselected as an output channel audio signal, it is able to generate anoutput channel audio signal of two channels L_(t) and R_(t).

If the left total channel L_(t), the center total channel C_(t) and theright total channel R_(t) are selected as an output channel audiosignal, it is able to generate an output channel audio signal of threechannels L_(t), C_(t) and R_(t).

In case that partial spatial information includes CLD₂ in addition,after upmixing has been performed up to a center channel C and a lowfrequency channel LFE, if the left total channel L_(t), the right totalchannel R_(t), the center channel C and the low frequency channel LFEare selected as an output channel audio signal, it is able to generatean output channel audio signal of four channels (L_(t), R_(t), C andLFE).

In the above description, the process for generating the output channelaudio signal by applying the spatial parameters in part only has beenexplained by taking the three kinds of tree configurations as examples.Besides, it is also able to additionally apply combined spatialinformation or extended spatial information as well as the partialspatial information. Thus, it is able to handle the process for applyingthe modified spatial information to the audio signal hierarchically orcollectively and synthetically.

(2) Combined Spatial Information

Since spatial information is calculated in the course of downmixing amulti-channel audio signal according to a predetermined treeconfiguration, an original multi-channel audio signal before downmixingcan be reconstructed if a downmix audio signal is decoded using spatialparameters of the spatial information as they are. In case that achannel number M of a multi-channel audio signal is different from achannel number N of an output channel audio signal, new combined spatialinformation is generated by combining spatial information and it is thenable to upmix the downmix audio signal using the generated information.In particular, by applying spatial parameters to a conversion formula,it is able to generate combined spatial parameters.

This method can be varied according to a sequence and method ofdownmixing a multi-channel audio signal in an encoding apparatus. And,it is able to inquire the downmixing sequence and method using treeconfiguration information of spatial information. And, this method canbe varied according to a number of output channels. Moreover, it is ableto inquire the number of output channels and the like using outputchannel information.

Hereinafter, detailed embodiments for a method of modifying spatialinformation and embodiments for giving a virtual 3-D effect areexplained in the following description.

(2)-1. General Combined Spatial Information

A method of generating combined spatial parameters by combining spatialparameters of spatial information is provided for the upmixing accordingto a tree configuration different from that in a downmixing process. So,this method is applicable to all kinds of downmix audio signals nomatter what a tree configuration according to tree configurationinformation is.

In case that a multi-channel audio signal is 5.1-channel and a downmixaudio signal is 1-channel (mono channel), a method of generating anoutput channel audio signal of two channels is explained with referenceto two kinds of examples as follows.

(2)-1-1. Fourth Embodiment of Tree Configuration (5-1-5₁ TreeConfiguration)

FIG. 5 is a schematic diagram of an example of applying combined spatialinformation.

Referring to a left part of FIG. 5, CLD₀ to CLD₄ and ICC₀ to ICC₄ (notshown in the drawing) can be called spatial parameters that can becalculated in a process for downmixing a multi-channel audio signal of5.1-channels. For instance, in spatial parameters, an inter-channellevel difference between a left channel signal L and a right channelsignal R is CLD₃ and inter-channel correlation between L and R is ICC₃.And, an inter-channel level difference between a left surround channelL_(s) and a right surround channel R_(s) is CLD₂ and inter-channelcorrelation between L_(s) and R_(s) is ICC₂.

On the other hand, referring to a right part of FIG. 5, if a leftchannel signal L_(t) and a right channel signal R_(t) are generated byapplying combined spatial parameters CLD_(α) and ICC_(α) to a monodownmix audio signal m, it is able to directly generate a stereo outputchannel audio signal L_(t) and R_(t) from the mono channel audio signalm. In this case, the combined spatial parameters CLD_(α) and ICC_(α) canbe calculated by combining the spatial parameters CLD₀ to CLD₄ and ICC₀to ICC₄.

Hereinafter, a process for calculating CLD_(α) among combined spatialparameters by combining CLD₀ to CLD₄ together is firstly explained, anda process for calculating ICC_(α) among combined spatial parameters bycombining CLD₀ to CLD₄ and ICC₀ to ICC₄ is then explained as follows.

(2)-1-1-a. Derivation of CLD_(α)

First of all, since CLD_(α) is a level difference between a left outputsignal L_(t) and a right output signal R_(t), a result from inputtingthe left output signal L_(t) and the right output signal R_(t) to adefinition formula of CLD is shown as follows.

CLD_(α)=10*log₁₀(P _(Lt) /P _(Rt))  [Formula 1]

where P_(Lt) is a power of L_(t) and P_(Rt) is a power of R_(t).

CLD_(α)=10*log₁₀(P _(Lt) +a/P _(Rt) +a)  [Formula 2]

where P_(Lt) is a power of L_(t), P_(Rt) is a power of R_(t), and ‘a’ isa very small constant.

Hence, CLD_(α) is defined as Formula 1 or Formula 2.

Meanwhile, in order to represent P_(Lt) and P_(Rt) using spatialparameters CLD₀ to CLD₄, a relation formula between a left output signalL_(t) of an output channel audio signal, a right output signal R_(t) ofthe output channel audio signal and a multi-channel signal L, L_(s), R,R_(s), C and LFE are needed. And, the corresponding relation formula canbe defined as follows.

L _(t) =L+L _(s) +C/√2+LFE/2

R _(t) =R+R _(s) +C/√2+LFE/2  [Formula 3]

Since the relation formula like Formula 3 can be varied according to howto define an output channel audio signal, it can be defined in a mannerof formula different from Formula 3. For instance, ‘1/√2’ in C/√2 orLFE/√2 can be ‘0’ or ‘1’.

Formula 3 can bring out Formula 4 as follows.

P _(Lt) =P _(L) +P _(Ls) +P _(C)/2+P _(LFE)/2

P _(Rt) =P _(R) +P _(Rs) +P _(C)/2+P _(LFE)/2  [Formula 4]

It is able to represent CLD_(α) according to Formula 1 or Formula 2using P_(Lt) and P_(Rt). And, ‘P_(Lt) and P_(Rt)’ can be representedaccording to Formula 4 using P_(L), P_(Ls), P_(C), P_(LFE), P_(R) andP_(Rs). So, it is needed to find a relation formula enabling the P_(L),P_(Ls), P_(C), P_(LFE), P_(R) and P_(Rs) to be represented using spatialparameters CLD₀ to CLD₄.

Meanwhile, in case of the tree configuration shown in FIG. 5, a relationbetween a multi-channel audio signal (L, R, C, LFE, L_(s), R_(s)) and amono downmixed channel signal m is shown as follows.

$\begin{matrix}{{\begin{bmatrix}L \\R \\C \\{LFE} \\{Ls} \\{Rs}\end{bmatrix} = {{\begin{bmatrix}D_{L} \\D_{R} \\D_{C} \\D_{LFE} \\D_{Ls} \\D_{Rs}\end{bmatrix}m} = {\begin{bmatrix}{c_{1,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{1,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{1,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}}\end{bmatrix}m}}}{{where},{c_{1,{OTT}_{x}} = \sqrt{\frac{10^{\frac{{CLD}_{x}}{l\; 0}}}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}},{c_{2,{OTT}_{x}} = {\sqrt{\frac{1}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}.}}}} & \left\{ {{Formula}\mspace{14mu} 5} \right\}\end{matrix}$

And, Formula 5 brings about Formula 6 as follows.

$\begin{matrix}{{\begin{bmatrix}P_{L} \\P_{R} \\P_{C} \\P_{LFE} \\P_{Ls} \\P_{Rs}\end{bmatrix} = {\begin{bmatrix}\left( {c_{1,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{1,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{1,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \right)^{2}\end{bmatrix}m^{2}}}{{where},{c_{1,{OTT}_{x}} = \sqrt{\frac{10^{\frac{{CLD}_{x}}{l\; 0}}}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}},{c_{2,{OTT}_{x}} = {\sqrt{\frac{1}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}.}}}} & \left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In particular, by inputting Formula 6 to Formula 4 and by inputtingFormula 4 to Formula 1 or Formula 2, it is able to represent thecombined spatial parameter CLD_(α) in a manner of combining spatialparameters CLD₀ to CLD₄.

Meanwhile, an expansion resulting from inputting Formula 6 toP_(C)/2+P_(LFE)/2 in Formula 4 is shown in Formula 7.

P _(C)/2+P _(LFE)/2=[(c _(1,OTT4))²+(c _(2,OTT4))²]*(c _(2,OTT1) *c_(1,OTT0))*m ²/2,  [Formula 7]

In this case, according to definitions of c₁ and c₂ (cf. Formula 5),since (c_(1,x))²+(c_(2,x))²=1, it results in(c_(1,OTT4))²+(c_(2,OTT4))²=1.

So, Formula 7 can be briefly summarized as follows.

P _(C)/2+P _(LFE)/2=(c _(2,OTT1) *c _(1,OTT0))² *m ²/2  [Formula 8]

Therefore, by inputting Formula 8 and Formula 6 to Formula 4 and byinputting Formula 4 to Formula 1, it is able to represent the combinedspatial parameter CLD₀ in a manner of combining spatial parameters CLD₀to CLD₄.

(2)-1-1-b. Derivation of ICC_(α)

First of all, since ICC_(α) is a correlation between a left outputsignal L_(t) and a right output signal R_(t), a result from inputtingthe left output signal L_(t) and the right output signal R_(t) to acorresponding definition formula is shown as follows.

$\begin{matrix}{{{{ICC}_{x} = \frac{P_{LtRt}}{\sqrt{P_{Lt}P_{Rt}}}},{where}}{P_{x_{1}x_{2}} = {\sum\limits^{\;}{x_{1}{x_{2}^{*}.}}}}} & \left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack\end{matrix}$

In Formula 9, P_(Lt) and P_(Rt) can be represented using CLD₀ to CLD₄ inFormula 4, Formula 6 and Formula 8. And, P_(Lt)P_(Rt) can be expanded ina manner of Formula 10.

P _(LtRt) =P _(LR) +P _(LsRs) +P _(C)/2+P _(LFE)/2  [Formula 10]

In Formula 10, ‘P_(C)/2+P_(LFE)/2’ can be represented as CLD₀ to CLD₄according to Formula 6. And, P_(LR) and P_(LsRs) can be expandedaccording to ICC definition as follows.

ICC₃ =P _(LR)/√(P _(L) P _(R))

ICC₂ =P _(LsRs)/√(P _(Ls) P _(Rs))  [Formula 11]

In Formula 11, if √(P_(L)P_(R)) or √(P_(Ls)P_(Rs)) is transposed,Formula 12 is obtained.

P _(LR)=ICC₃*√(P _(L) P _(R))

P _(LsRs)=ICC₂*√(P _(Ls) P _(Rs))  [Formula 12]

In Formula 12, P_(L), P_(R), P_(Ls) and P_(Rs) can be represented asCLD₀ to CLD₄ according to Formula 6. A formula resulting from inputtingFormula 6 to Formula 12 corresponds to Formula 13.

P _(LR)=ICC₃ *c _(1,OTT3) *c _(2,OTT3)*(c _(1,OTT1) *c _(1,OTT0))² *m ²

P _(LsRs)=ICC₂ *c _(1,OTT2) *c _(2,OTT2)*(c _(2,OTT0))² *m ²  [Formula13]

In summary, by inputting Formula 6 and Formula 13 to Formula 10 and byinputting Formula 10 and Formula 4 to Formula 9, it is able to representa combined spatial parameter ICC_(α) as spatial parameters CLD₀ to CLD₃,ICC₂ and ICC₃.

(2)-1-2. Fifth Embodiment of Tree Configuration (5-1-5₂ TreeConfiguration)

FIG. 6 is a schematic diagram of another example of applying combinedspatial information.

Referring to a left part of FIG. 6, CLD₀ to CLD₄ and ICC₀ to ICC₄ (notshown in the drawing) can be called spatial parameters that can becalculated in a process for downmixing a multi-channel audio signal of5.1-channels.

In the spatial parameters, an inter-channel level difference between aleft channel signal L and a left surround channel signal Ls is CLD₃ andinter-channel correlation between L and L_(s) is ICC₃. And, aninter-channel level difference between a right channel R and a rightsurround channel R_(s) is CLD₄ and inter-channel correlation between Rand R_(s) is ICC₄.

On the other hand, referring to a right part of FIG. 6, if a leftchannel signal L_(t) and a right channel signal R_(t) are generated byapplying combined spatial parameters CLD_(β) and ICC_(β) to a monodownmix audio signal m, it is able to directly generate a stereo outputchannel audio signal L_(t) and R_(t) from the mono channel audio signalm. In this case, the combined spatial parameters CLD_(β) and ICC_(β) canbe calculated by combining the spatial parameters CLD₀ to CLD₄ and ICC₀to ICC₄.

Hereinafter, a process for calculating CLD_(β) among combined spatialparameters by combining CLD₀ to CLD₄ is firstly explained, and a processfor calculating ICC_(β) among combined spatial parameters by combiningCLD₀ to CLD₄ and ICC₀ to ICC₄ is then explained as follows.

(2)-1-2-a. Derivation of CLD_(β)

First of all, since CLD_(β) is a level difference between a left outputsignal L_(t) and a right output signal R_(t), a result from inputtingthe left output signal L_(t) and the right output signal R_(t) to adefinition formula of CLD is shown as follows.

CLD_(β)=10*log₁₀(P _(Lt) /P _(Rt)),  [Formula 14]

where P_(Lt) is a power of L_(t) and P_(Rt) is a power of R_(t).

CLD_(β)=10*log₁₀(P _(Lt) +a/P _(Rt) +a),  [Formula 15]

where P_(Lt) is a power of L_(t), P_(Rt) is a power of R_(t), and ‘a’ isa very small number.

Hence, CLD_(β) is defined as Formula 14 or Formula 15.

Meanwhile, in order to represent P_(Lt) and P_(Rt) using spatialparameters CLD₀ to CLD₄, a relation formula between a left output signalL_(t) of an output channel audio signal, a right output signal R_(t) ofthe output channel audio signal and a multi-channel signal L, L_(s), R,R_(s), C and LFE are needed. And, the corresponding relation formula canbe defined as follows.

L _(t) =L+L _(s) +C/√2+LFE/√2

R _(t) =R+R _(s) +C/√2+LFE/√2  [Formula 16]

Since the relation formula like Formula 16 can be varied according tohow to define an output channel audio signal, it can be defined in amanner of formula different from Formula 16. For instance, ‘1/√2’ inC/√2 or LFE/√2 can be ‘0’ or ‘1’.

Formula 16 can bring out Formula 17 as follows.

P _(Lt) =P _(L) +P _(Ls) +P _(C)/2+P _(LFE)/2

P _(Rt) =P _(R) +P _(Rs) +P _(C)/2+P _(LFE)/2  [Formula 17]

It is able to represent CLD_(β) according to Formula 14 or Formula 15using P_(Lt) and P_(Rt). And, ‘P_(Lt) and P_(Rt)’ can be representedaccording to Formula 15 using P_(L), P_(Ls), P_(C), P_(LFE), P_(R) andP_(Rs). So, it is needed to find a relation formula enabling the P_(L),P_(Ls), P_(C), P_(LFE), P_(R) and P_(Rs) to be represented using spatialparameters CLD₀ to CLD₄.

Meanwhile, in case of the tree configuration shown in FIG. 6, therelation between a multi-channel audio signal (L, R, C, LFE, L_(s),R_(s)) and a mono downmixed channel signal m is shown as follows.

$\begin{matrix}{{{\begin{bmatrix}L \\{Ls} \\R \\{Rs} \\C \\{LFE}\end{bmatrix} = {{\begin{bmatrix}D_{L} \\D_{Ls} \\D_{R} \\D_{Rs} \\D_{C} \\D_{LFE}\end{bmatrix}m} = {\begin{bmatrix}{c_{1,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{1,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \\{c_{1,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \\{c_{2,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}}\end{bmatrix}m}}},{where}}{{c_{1,{OTT}_{x}} = \sqrt{\frac{10^{\frac{{CLD}_{x}}{l\; 0}}}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}},{c_{2,{OTT}_{x}} = {\sqrt{\frac{1}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}.}}}} & \left\{ {{Formula}\mspace{14mu} 18} \right\}\end{matrix}$

And, Formula 18 brings about Formula 19 as follows.

$\begin{matrix}{{\begin{bmatrix}P_{L} \\P_{Ls} \\P_{R} \\P_{Rs} \\P_{C} \\P_{LFE}\end{bmatrix} = {\begin{bmatrix}\left( {c_{1,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 3}}c_{1,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{1,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 4}}c_{2,{{OTT}\; 1}}c_{1,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{1,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \right)^{2} \\\left( {c_{2,{{OTT}\; 2}}c_{2,{{OTT}\; 0}}} \right)^{2}\end{bmatrix}m^{2}}},{where},{c_{1,{OTT}_{x}} = \sqrt{\frac{10^{\frac{{CLD}_{x}}{l\; 0}}}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}},{c_{2,{OTT}_{x}} = {\sqrt{\frac{1}{1 + 10^{\frac{{CLD}_{x}}{l\; 0}}}}.}}} & \left\lbrack {{Formula}\mspace{14mu} 19} \right\rbrack\end{matrix}$

In particular, by inputting Formula 19 to Formula 17 and by inputtingFormula 17 to Formula 14 or Formula 15, it is able to represent thecombined spatial parameter CLD_(β) in a manner of combining spatialparameters CLD₀ to CLD₄.

Meanwhile, an expansion formula resulting from inputting Formula 19 toP_(L)+P_(Ls) in Formula 17 is shown in Formula 20.

P _(L) +P _(Ls)=[(c _(1,OTT3))²+(c _(2,OTT3))²](c _(1,OTT1) *c_(1,OTT0))² *m ²  [Formula 20]

In this case, according to definitions of c₁ and c₂ (cf. Formula 5),since (c_(1,x))²+(c_(2,x))²=1, it results in(c_(1,OTT3))²+(c_(2,OTT3))²=1.

So, Formula 20 can be briefly summarized as follows.

P _(L) _(—) =P _(L) +P _(Ls)=(c _(1,OTT1) *c _(1,OTT0))² *m ²  [Formula21]

On the other hand, an expansion formula resulting from inputting Formula19 to P_(R)+P_(Rs) in Formula 17 is shown in Formula 22.

P _(R) +P _(Rs)=[(c _(1,OTT4))+(c _(2,OTT4))²](c _(1,OTT1) *c_(1,OTT0))² *m ²  [Formula 22]

In this case, according to definitions of c₁ and c₂ (cf. Formula 5),since (c_(1,x))²+(c_(2,x))²=1, it results in(c_(1,OTT4))²+(c_(2,OTT4))²=1.

So, Formula 22 can be briefly summarized as follows.

P _(R) _(—) =P _(R) +P _(Rs)=(c _(2,OTT1) *c _(1,OTT0))² *m ²  [Formula23]

On the other hand, an expansion formula resulting from inputting Formula19 to P_(C)/2+P_(LFE)/2 in Formula 17 is shown in Formula 24.

P _(C)/2+P _(LFE)/2=[(c _(1,OTT2))²+(c _(2,OTT2))²](c _(2,OTT0))² *m²/2  [Formula 24]

In this case, according to definitions of c₁ and c₂ (cf. Formula 5),since (c_(1,x))²+(c_(2,x))²=1, it results in(c_(1,OTT2))²+(c_(2,OTT2))²=1.

So, Formula 24 can be briefly summarized as follows.

P _(C)/2+P _(LFE)/2=(c _(2,OTT0))² *m ²/2  [Formula 25]

Therefore, by inputting Formula 21, formula 23 and Formula 25 to Formula17 and by inputting Formula 17 to Formula 14 or Formula 15, it is ableto represent the combined spatial parameter CLD_(β) in a manner ofcombining spatial parameters CLD₀ to CLD₄.

(2)-1-2-b. Derivation of ICC_(β)

First of all, since ICC_(β) is a correlation between a left outputsignal L_(t) and a right output signal R_(t), a result from inputtingthe left output signal L_(t) and the right output signal R_(t) to acorresponding definition formula is shown as follows.

$\begin{matrix}{{{{ICC}_{x} = \frac{P_{LtRt}}{\sqrt{P_{Lt}P_{Rt}}}},{where}}{P_{x_{1}x_{2}} = {\sum\limits^{\;}{x_{1}{x_{2}^{*}.}}}}} & \left\lbrack {{Formula}\mspace{14mu} 26} \right\rbrack\end{matrix}$

In Formula 26, P_(Lt) and P_(Rt) can be represented according to Formula19 using CLD₀ to CLD₄. And. P_(Lt)P_(Rt) can be expanded in a manner ofFormula 27.

P _(LtRt) =P _(L) _(—) _(R) _(—) +P _(C)/2+P _(LFE)/2  [Formula 27]

In Formula 27, ‘P_(C)/2+P_(LFE)/2’ can be represented as CLD₀ to CLD₄according to Formula 19. And, P_(L) _(—) _(R) _(—) can be expandedaccording to ICC definition as follows.

ICC₁ =P _(L) _(—) _(R) _(—) /√(P _(L) _(—) P _(R) _(—) )  [Formula 28]

If √(P_(L) _(—) P_(R) _(—) ) is transposed, Formula 29 is obtained.

P _(L) _(—) _(R) _(—) =ICC₁*√(P _(L) _(—) P _(R) _(—) )  [Formula 29]

In Formula 29, P_(L) _(—) and P_(R) _(—) can be represented as CLD₀ toCLD₄ according to Formula 21 and Formula 23. A formula resulting frominputting Formula 21 and Formula 23 to Formula 29 corresponds to Formula30.

P _(L) _(—) _(R) _(—) =ICC₁ *c _(1,OTT1) *c _(1,OTT0) *c _(2,OTT1) *c_(1,OTT0) *m ²  [Formula 30]

In summary, by inputting Formula 30 to Formula 27 and by inputtingFormula 27 and Formula 17 to Formula 26, it is able to represent acombined spatial parameter ICC_(β) as spatial parameters CLD₀ to CLD₄and ICC₁.

The above-explained spatial parameter modifying methods are just oneembodiment. And, in finding P_(x) or P_(xy), it is apparent that theabove-explained formulas can be varied in various forms by consideringcorrelations (e.g., ICC₀, etc.) between the respective channels as wellas signal energy in addition.

(2)-2. Combined Spatial Information Having Surround Effect

First of all, in case of considering sound paths to generate combinedspatial information by combining spatial information, it is able tobring about a virtual surround effect.

The virtual surround effect or virtual 3D effect is able to bring aboutan effect that there substantially exists a speaker of a surroundchannel without the speaker of the surround channel. For instance,5.1-channel audio signal is outputted via two stereo speakers.

A sound path may correspond to spatial filter information. The spatialfilter information is able to use a function named HRTF (head-relatedtransfer function), which is not limited by the present invention. Thespatial filter information is able to include a filter parameter. Byinputting the filter parameter and spatial parameters to a conversionformula, it is able to generate a combined spatial parameter. And, thegenerated combined spatial parameter may include filter coefficients.

Hereinafter, assuming that a multi-channel audio signal is 5-channelsand that an output channel audio signal of three channels is generated,a method of considering sound paths to generate combined spatialinformation having a surround effect is explained as follows.

FIG. 7 is a diagram of sound paths from speakers to a listener, in whichpositions of the speakers are shown.

Referring to FIG. 7, positions of three speakers SPK1, SPK2 and SPK3 areleft front L, center C and right R, respectively. And, positions ofvirtual surround channels are left surround Ls and right surround Rs,respectively.

Sound paths to positions r and l of right and left ears of a listenerfrom the positions L, C and R of the three speakers and positions Ls andRs of virtual surround channels, respectively are shown. An indicationof ‘G_(x) _(—) _(y)’ indicates the sound path from the position x to theposition y. For instance, an indication of ‘G_(L) _(—) _(r)’ indicatesthe sound path from the position of the left front L to the position ofthe right ear r of the listener.

If there exist speakers at five positions (i.e., speakers exist at leftsurround Ls and right surround Rs as well) and if the listener exists atthe position shown in FIG. 7, a signal L₀ introduced into the left earof the listener and a signal R₀ introduced into the right ear of thelistener are represented as Formula 31.

L _(o) =L*G _(L) _(—) _(l) +C*G _(C) _(—) _(l) +R*G _(R) _(—) _(l) +Ls*G_(Ls) _(—) _(l) +Rs*G _(Rs) _(—) _(l)

R _(o) =L*G _(L) _(—) _(r) +C*G _(C) _(—) _(r) +R*G _(R) _(—) _(r) +Ls*G_(Ls) _(—) _(r) +Rs*G _(Rs) _(—) _(r),  [Formula 31]

where L, C, R, Ls and Rs are channels at positions, respectively, G_(x)_(—) _(y) indicates a sound path from a position x to a position y, and‘*’ indicates a convolution.

Yet, as mentioned in the foregoing description, in case that thespeakers exist at the three positions L, C and R only, a signal L₀ _(—)_(real) introduced into the left ear of the listener and a signal R₀_(—) _(real) introduced into the right ear of the listener arerepresented as follows.

L _(o) _(—) _(real) =L*G _(L) _(—) _(l) +C*G _(C) _(—) _(l) +R*G _(R)_(—) _(l)

R _(o) _(—) _(real) =L*G _(L) _(—) _(r) +C*G _(C) _(—) _(r) +R*G _(R)_(—) _(r)  [Formula 32]

Since surround channel signals Ls and Rs are not taken intoconsideration by the signals shown in Formula 32, it is unable to bringabout a virtual surround effect. In order to bring about the virtualsurround effect, a Ls signal arriving at the position (l, r) of thelistener from the speaker position Ls is made equal to a Ls signalarriving at the position (l, r) of the listener from the speaker at eachof the three positions L, C and R different from the original positionLs. And, this is identically applied to the case of the right surroundchannel signal Rs as well.

Looking into the left surround channel signal Ls, in case that the leftsurround channel signal Ls is outputted from the speaker at the leftsurround position Ls as an original position, signals arriving at theleft and right ears l and r of the listener are represented as follows.

‘Ls*G_(Ls) _(—) _(l)’, ‘Ls*G_(Ls) _(—) _(r)’  [Formula 33]

And, in case that the right surround channel signal Rs is outputted fromthe speaker at the right surround position Rs as an original position,signals arriving at the left and right ears l and r of the listener arerepresented as follows.

‘Rs*G_(Rs) _(—) _(l)’, ‘Rs*G_(Rs) _(—) _(r)’  [Formula 34]

In case that the signals arriving at the left and right ears l and r ofthe listener are equal to components of Formula 33 and Formula 34, evenif they are outputted via the seakers of any position (e.g., via thespeaker SPK1 at the left front position), the listener is able to senseas if speakers exist at the left and right surround positions Ls and Rs,respectively.

Meanwhile, in case that components shown in Formula 33 are outputtedfrom the speaker at the left surround position Ls, they are the signalsarriving at the left and right ears l and r of the listener,respectively. So, if the components shown in Formula 33 are outputtedintact from the speaker SPK1 at the left front position, signalsarriving at the left and right ears l and r of the listener can berepresented as follows.

‘Ls*G_(Ls) _(—) _(l)*G_(L) _(—) _(l)’, ‘Ls*G_(Ls) _(—) _(r)*G_(L) _(—)_(r)’  [Formula 35]

Looking into Formula 35, a component ‘G_(L) _(—) _(l)’ (or ‘G_(L) _(—)_(r)’) corresponding to the sound path from the left front position L tothe left ear l (or the right ear r) of the listener is added.

Yet, the signals arriving at the left and right ears l and r of thelistener should be the components shown in Formula 33 instead of Formula35. In case that a sound outputted from the speaker at the left frontposition L arrives at the listener, the component ‘G_(L) _(—) _(l)’ (or‘G_(L) _(—) _(r)’) is added. So, if the components shown in Formula 33are outputted from the speaker SPK1 at the left front position, aninverse function ‘G_(L) _(—) _(l) ⁻¹’ (or ‘G_(L) _(—) _(r) ⁻¹’) of the‘G_(L) _(—) _(l)’ (or ‘G_(L) _(—) _(r)’) should be taken intoconsideration for the sound path. In other words, in case that thecomponents corresponding to Formula 33 are outputted from the speakerSPK1 at the left front position L, they have to be modified as thefollowing formula.

‘Ls*G_(Ls) _(—) _(l)*G_(L) _(—) _(l) ⁻¹’, ‘Ls*G_(Ls) _(—) _(r)*G_(L)_(—) _(r) ⁻¹’  [Formula 36]

And, in case that the components corresponding to Formula 34 areoutputted from the speaker SPK1 at the left front position L, they haveto be modified as the following formula.

‘Rs*G_(Rs) _(—) _(l)*G_(L) _(—) _(l) ⁻¹’, ‘Rs*G_(Rs) _(—) _(r)*G_(L)_(—) _(l) ⁻¹’  [Formula 37]

So, the signal L′ outputted from the speaker SPK1 at the left frontposition L is summarized as follows.

L′=L+Ls*G _(Ls) _(—) _(l) *G _(L) _(—) _(l) ⁻¹ +Rs*G _(Rs) _(—) _(r) *G_(L) _(—) _(l) ⁻¹  [Formula 38]

(Components Ls*G_(Ls) _(—) _(r)*G_(L) _(—) _(r) and Rs*G_(Rs) _(—)_(r)*G_(L) _(—) _(l) ⁻¹ are omitted.)

If the signal, which is shown in Formula 38 to be outputted from thespeaker SPK1 at the left front position L, arrives at the position ofthe left ear L of the listener, a sound path factor ‘G_(L) _(—) _(l)’ isadded. So, ‘G_(L) _(—) _(l)’ terms in formula 38 are cancelled out,whereby factors shown in Formula 33 and Formula 34 eventually remain.

FIG. 8 is a diagram to explain a signal outputted from each speakerposition for a virtual surround effect.

Referring to FIG. 8, if signals Ls and Rs outputted from surroundpositions Ls and Rs are made to be included in a signal L′ outputtedfrom each speaker position SPK1 by considering sound paths, theycorrespond to Formula 38.

In Formula 38, G_(Ls) _(—) _(l)*G_(L) _(—) _(l) ⁻¹ is brieflyabbreviated H_(Ls) _(—) _(L) as follows.

L′=L+Ls*H _(Ls) _(—) _(L) +Rs*H _(Rs) _(—L)   [Formula 39]

For instance, a signal C′ outputted from a speaker SPK2 at a centerposition C is summarized as follows.

C′=C+Ls*H _(Ls) _(—) _(C) +Rs*H _(Rs) _(—) _(C)  [Formula 40]

For another instance, a signal R′ outputted from a speaker SPK3 at aright front position R is summarized as follows.

R′=R+Ls*H _(Ls) _(—) _(R) +Rs*H _(Rs) _(—) _(R)  [Formula 41]

FIG. 9 is a conceptional diagram to explain a method of generating a3-channel signal using a 5-channel signal like Formula 38, Formula 39 orFormula 40.

In case of generating a 2-channel signal R′ and L′ using a 5-channelsignal or in case of not including a surround channel signal Ls or Rs ina center channel signal C′, H_(Ls) _(—) _(C) or H_(Rs) _(—) _(C) becomes0.

For convenience of implementation, H_(x) _(—) _(y) can be variouslymodified in such a manner that H_(x) _(—) _(y) is replaced by G_(x) _(—)_(y) or that H_(x) _(—) _(y) is used by considering cross-talk.

The above detailed explanation relates to one example of the combinedspatial information having the surround effect. And, it is apparent thatit can be varied in various forms according to a method of applyingspatial filter information. As mentioned in the foregoing description,the signals outputted via the speakers (in the above example, left frontchannel L′, right front channel R′ and center channel C′) according tothe above process can be generated from the downmix audio signal usingthe combined spatial information, an more particularly, using thecombined spatial parameters.

(3) Expanded Spatial Information

First of all, by adding extended spatial information to spatialinformation, it is able to generate expanded spatial information. And,it is able to upmix an audio signal using the extended spatialinformation. In the corresponding upmixing process, an audio signal isconverted to a primary upmixing audio signal based on spatialinformation and the primary upmixing audio signal is then converted to asecondary upmixing audio signal based on extended spatial information.

In this case, the extended spatial information is able to includeextended channel configuration information, extended channel mappinginformation and extended spatial parameters.

The extended channel configuration information is information for aconfigurable channel as well as a channel that can be configured by treeconfiguration information of spatial information. The extended channelconfiguration information may include at least one of a divisionidentifier and a non-division identifier, which will be explained indetail later. The extended channel mapping information is positioninformation for each channel that configures an extended channel. And,the extended spatial parameters can be used for upmixing one channelinto at least two channels. The extended spatial parameters may includeinter-channel level differences.

The above-explained extended spatial information may be included inspatial information after having been generated by an encoding apparatus(i) or generated by a decoding apparatus by itself (ii). In case thatextended spatial information is generated by an encoding apparatus, apresence or non-presence of the extended spatial information can bedecided based on an indicator of spatial information. In case thatextended spatial information is generated by a decoding apparatus byitself, extended spatial parameters of the extended spatial informationmay result from being calculated using spatial parameters of spatialinformation.

Meanwhile, a process for upmixing an audio signal using the expandedspatial information generated on the basis of the spatial informationand the extended spatial information can be executed sequentially andhierarchically or collectively and synthetically. If the expandedspatial information can be calculated as one matrix based on spatialinformation and extended spatial information, it is able to upmix adownmix audio signal into a multi-channel audio signal collectively anddirectly using the matrix. In this case, factors configuring the matrixcan be defined according to spatial parameters and extended spatialparameters.

Hereinafter, after completion of explaining a case that extended spatialinformation generated by an encoding apparatus is used, a case ofgenerating extended spatial information in a decoding apparatus byitself will be explained.

(3)-1: Case of Using Extended Spatial Information Generated by EncodingApparatus: Arbitrary Tree Configuration

First of all, expanded spatial information is generated by an encodingapparatus in being generated by adding extended spatial information tospatial information. And, a case that a decoding apparatus receives theextended spatial information will be explained. Besides, the extendedspatial information may be the one extracted in a process that theencoding apparatus downmixes a multi-channel audio signal.

As mentioned in the foregoing description, extended spatial informationincludes extended channel configuration information, extended channelmapping information and extended spatial parameters. In this case, theextended channel configuration information may include at least one of adivision identifier and a non-division identifier. Hereinafter, aprocess for configuring an extended channel based on array of thedivision and non-division identifiers is explained in detail as follows.

FIG. 10 is a diagram of an example of configuring extended channelsbased on extended channel configuration information.

Referring to a lower end of FIG. 10, 0's and 1's are repeatedly arrangedin a sequence. In this case, ‘0’ means a non-division identifier and ‘1’means a division identifier. A non-division identifier 0 exists in afirst order (1), a channel matching the non-division identifier 0 of thefirst order is a left channel L existing on a most upper end. So, theleft channel L matching the non-division identifier 0 is selected as anoutput channel instead of being divided. In a second order (2), thereexists a division identifier 1. A channel matching the divisionidentifier is a left surround channel Ls next to the left channel L. So,the left surround channel Ls matching the division identifier 1 isdivided into two channels.

Since there exist non-division identifiers 0 in a third order (3) and afourth order (4), the two channels divided from the left surroundchannel Ls are selected intact as output channels without being divided.Once the above process is repeated to a last order (10), it is able toconfigure entire extended channels.

The channel dividing process is repeated as many as the number ofdivision identifiers 1, and the process for selecting a channel as anoutput channel is repeated as many as the number of non-divisionidentifiers 0. So, the number of channel dividing units AT0 and AT1 areequal to the number (2) of the division identifiers 1, and the number ofextended channels (L, Lfs, Ls, R, Rfs, Rs, C and LFE) are equal to thenumber (8) of non-division identifiers 0.

Meanwhile, after the extend channel has been configured, it is able tomap a position of each output channel using extended channel mappinginformation. In case of FIG. 10, mapping is carried out in a sequence ofa left front channel L, a left front side channel Lfs, a left surroundchannel Ls, a right front channel R, a right front side channel Rfs, aright surround channel Rs, a center channel C and a low frequencychannel LFS.

As mentioned in the foregoing description, an extended channel can beconfigured based on extended channel configuration information. Forthis, a channel dividing unit dividing one channel into at least twochannels is necessary. In dividing one channel into at least twochannels, the channel dividing unit is able to use extended spatialparameters. Since the number of the extended spatial parameters is equalto that of the channel dividing units, it is equal to the number ofdivision identifiers as well. So, the extended spatial parameters can beextracted as many as the number of the division identifiers.

FIG. 11 is a diagram to explain a configuration of the extended channelsshown in FIG. 10 and the relation with extended spatial parameters.

Referring to FIG. 11, there are two channel division units AT₀ and AT₁and extended spatial parameters ATD₀ and ATD₁ applied to them,respectively are shown.

In case that an extended spatial parameter is an inter-channel leveldifference, a channel dividing unit is able to decide levels of twodivided channels using the extended spatial parameter.

Thus, in performing upmixing by adding extended spatial information, theextended spatial parameters can be applied not entirely but partially.

(3)-2. Case of Generating Extended Spatial Information:Interpolation/Extrapolation

First of all, it is able to generate expanded spatial information byadding extended spatial information to spatial information. A case ofgenerating extended spatial information using spatial information willbe explained in the following description. In particular, it is able togenerate extended spatial information using spatial parameters ofspatial information. In this case, interpolation, extrapolation or thelike can be used.

(3)-2-1. Extension to 6.1-Channels

In case that a multi-channel audio signal is 5.1-channels, a case ofgenerating an output channel audio signal of 6.1-channels is explainedwith reference to examples as follows.

FIG. 12 is a diagram of a position of a multi-channel audio signal of5.1-channels and a position of an output channel audio signal of6.1-channels.

Referring to (a) of FIG. 12, it can be seen that channel positions of amulti-channel audio signal of 5.1-channels are a left front channel L, aright front channel R, a center channel C, a low frequency channel (notshown in the drawing) LFE, a left surround channel Ls and a rightsurround channel Rs, respectively.

In case that the multi-channel audio signal of 5.1-channels is a downmixaudio signal, if spatial parameters are applied to the downmix audiosignal, the downmix audio signal is upmixed into the multi-channel audiosignal of 5.1-channels again.

Yet, a channel signal of a rear center RC, as shown in (b) of FIG. 12,should be further generated to upmix a downmix audio signal into amulti-channel audio signal of 6.1-channels.

The channel signal of the rear center RC can be generated using spatialparameters associated with two rear channels (left surround channel Lsand right surround channel Rs). In particular, an inter-channel leveldifference (CLD) among spatial parameters indicates a level differencebetween two channels. So, by adjusting a level difference between twochannels, it is able to change a position of a virtual sound sourceexisting between the two channels.

A principle that a position of a virtual sound source varies accordingto a level difference between two channels is explained as follows.

FIG. 13 is a diagram to explain the relation between a virtual soundsource position and a level difference between two channels, in whichlevels of left and surround channels Ls and RS are ‘a’ and ‘b’,respectively.

Referring to (a) of FIG. 13, in case that a level a of a left surroundchannel Ls is greater than that b of a right surround channel Rs, it canbe seen that a position of a virtual sound source VS is closer to aposition of the left surround channel LS than a position of the rightsurround channel Rs.

If an audio signal is outputted from two channels, a listener feels thata virtual sound source substantially exists between the two channels. Inthis case, a position of the virtual sound source is closer to aposition of the channel having a level higher than that of the otherchannel.

In case of (b) of FIG. 13, since a level a of a left surround channel Lsis almost equal to a level b of a right surround channel Rs, a listenerfeels that a position of a virtual sound source exists at a centerbetween the left surround channel Ls and the right surround channel Rs.

Hence, it is able to decide a level of a rear center using the aboveprinciple.

FIG. 14 is a diagram to explain levels of two rear channels and a levelof a rear center channel.

Referring to FIG. 14, it is able to calculate a level c of a rear centerchannel RC by interpolating a difference between a level a of a leftsurround channel Ls and a level b of a right surround channel Rs. Inthis case, non-linear interpolation can be used as well as linearinterpolation for the calculation.

A level c of a new channel (e.g., rear center channel RC) existingbetween two channels (e.g., Ls and Rs) can be calculated according tolinear interpolation by the following formula.

c=a*k+b*(1−k),  [Formula 40]

where ‘a’ and ‘b’ are levels of two channels, respectively and ‘k’ is arelative position beta channel of level-a, a channel of level-b and achannel of level-c.

If a channel (e.g., rear center channel RC) at a level-c is located at acenter between a channel (e.g., Ls) at a level-a and a channel RS at alevel-b, ‘k’ is 0.5. If ‘k’ is 0.5, Formula 40 follows Formula 41.

c=(a+b)/2  [Formula 41]

According to Formula 41, if a channel (e.g., rear center channel RC) ata level-c is located at a center between a channel (e.g., Ls) at alevel-a and a channel RS at a level-b, a level-c of a new channelcorresponds to a mean value of levels a and b of previous channels.Besides, Formula 40 and Formula 41 are just exemplary. So, it is alsopossible to readjust a decision of a level-c and values of the level-aand level-b.

(3)-2-2. Extension to 7.1-Channels

When a multi-channel audio signal is 5.1-channels, a case of attemptingto generate an output channel audio signal of 7.1-channels is explainedas follows.

FIG. 15 is a diagram to explain a position of a multi-channel audiosignal of 5.1-channels and a position of an output channel audio signalof 7.1-channels.

Referring to (a) of FIG. 15, like (a) of FIG. 12, it can be seen thatchannel positions of a multi-channel audio signal of 5.1-channels are aleft front channel L, a right front channel R, a center channel C, a lowfrequency channel (not shown in the drawing) LFE, a left surroundchannel Ls and a right surround channel Rs, respectively.

In case that the multi-channel audio signal of 5.1-channels is a downmixaudio signal, if spatial parameters are applied to the downmix audiosignal, the downmix audio signal is upmixed into the multi-channel audiosignal of 5.1-channels again.

Yet, a left front side channel Lfs and a right front side channel Rfs,as shown in (b) of FIG. 15, should be further generated to upmix adownmix audio signal into a multi-channel audio signal of 7.1-channels.

Since the left front side channel Lfs is located between the left frontchannel L and the left surround channel Ls, it is able to decide a levelof the left front side channel Lfs by interpolation using a level of theleft front channel L and a level of the left surround channel Ls.

FIG. 16 is a diagram to explain levels of two left channels and a levelof a left front side channel (Lfs).

Referring to FIG. 16, it can be seen that a level c of a left front sidechannel Lfs is a linearly interpolated value based on a level a of aleft front channel L and a level b of a left surround channel LS.

Meanwhile, although a left front side channel Lfs is located between aleft front channel L and a left surround channel Ls, it can be locatedoutside a left front channel L, a center channel C and a right frontchannel R. So, it is able to decide a level of the left front sidechannel Lfs by extrapolation using levels of the left front channel L,center channel C and right front channel R.

FIG. 17 is a diagram to explain levels of three front channels and alevel of a left front side channel.

Referring to FIG. 17, it can be seen that a level d of a left front sidechannel Lfs is a linearly extrapolated value based on a level a of aleft front channel 1, a level c of a center channel C and a level b of aright front channel.

In the above description, the process for generating the output channelaudio signal by adding extended spatial information to spatialinformation has been explained with reference to two examples. Asmentioned in the foregoing description, in the upmixing process withaddition of extended spatial information, extended spatial parameterscan be applied not entirely but partially. Thus, a process for applyingspatial parameters to an audio signal can be executed sequentially andhierarchically or collectively and synthetically.

INDUSTRIAL APPLICABILITY

Accordingly, the present invention provides the following effects.

First of all, the present invention is able to generate an audio signalhaving a configuration different from a predetermined treeconfiguration, thereby generating variously configured audio signals.

Secondly, since it is able to generate an audio signal having aconfiguration different from a predetermined tree configuration, even ifthe number of multi-channels before the execution of downmixing issmaller or greater than that of speakers, it is able to generate outputchannels having the number equal to that of speakers from a downmixaudio signal.

Thirdly, in case of generating output channels having the number smallerthan that of multi-channels, since a multi-channel audio signal isdirectly generated from a downmix audio signal instead of downmixing anoutput channel audio signal from a multi-channel audio signal generatedfrom upmixing a downmix audio signal, it is able to considerably reduceload of operations required for decoding an audio signal.

Fourthly, since sound paths are taken into consideration in generatingcombined spatial information, the present invention provides apseudo-surround effect in a situation that a surround channel output isunavailable.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1. A method of decoding an audio signal, comprising: receiving spatialinformation; generating combined spatial information using the spatialinformation; and decoding the audio signal using the combined spatialinformation, wherein the combined spatial information is generated bycombining spatial parameters included in the spatial information.
 2. Themethod of claim 1, wherein the combined spatial parameters are generatedby inputting the spatial parameters to a conversion formula.
 3. Themethod of claim 2, further comprising deciding the conversion formulaaccording to tree configuration information for the audio signal.
 4. Themethod of claim 2, further comprising deciding the conversion formulaaccording to output channel information.
 5. The method of claim 1,wherein the audio signal is a downmix audio signal generated fromdownmixing a multi-channel audio signal, and the spatial parameters aredecided in the course of downmixing the multi-channel audio signalaccording to a predetermined tree configuration.
 6. The method of claim1, wherein the audio signal is a signal generated from downmixing amulti-channel audio signal, the spatial parameters include aninter-channel level difference of the multi-channel audio signal, and aninter-channel level difference of combined spatial parameters iscalculated by combining the inter-channel level difference of themulti-channel audio signal entirely or partially.
 7. The method of claim1, wherein the audio signal is a signal generated from downmixing amulti-channel audio signal, the spatial parameters include at least oneof an inter-channel correlation of the multi-channel audio signal, andan inter-channel correlation of combined spatial parameters arecalculated by combining the inter-channel correlation of themulti-channel audio signal.
 8. The method of claim 7, wherein thespatial parameters further include an inter-channel level difference ofthe multi-channel audio signal, and the inter-channel correlation of thecombined spatial parameters are calculated by combining at least one ofthe inter-channel level difference of the multi-channel audio signal andat least one of the inter-channel level difference of the multi-channelaudio signal.
 9. The method of claim 1, wherein modified spatialinformation including the combined spatial information is generatedusing the spatial information and the modified spatial informationincludes at least one of partial spatial information and expandedspatial information.